(1) Field of the Invention
The present invention relates to an apparatus for detecting the position of a notch in a semiconductor wafer, and more particularly to an apparatus for detecting position in a V-shaped notch formed peripherally of a semiconductor wafer.
(2) Description of the Prior Art
Usually, semiconductor wafers are formed with what is called an orientation flat shaped by linearly cutting out a peripheral edge thereof, which is used in setting the wafers to a predetermined position. Japanese Patent Publication (Unexamined) No. 3-73553, for example, discloses a wafer position detecting apparatus which detects the position of an orientation flat as follows. First, a wafer having an orientation flat is rotated stepwise through predetermined angles on a rotating device. At stops of the rotation, outer peripheral positional data of the wafer are successively obtained by means of a one-dimensional image sensor. These outer peripheral positional data are stored in relation to angles of displacement of respective sampling points. Then, two sampling points are determined as having therebetween a sampling point providing the largest of all the outer peripheral positional data stored (i.e. a maximum distance from a predetermined position radially outwardly of the wafer to an opposite peripheral position of the wafer as detected by the one-dimensional image sensor). An angle of displacement, from a reference point, of a perpendicular extending from the center of rotation to the orientation flat is derived from the displacement angles and outer peripheral positional data of the two sampling points.
The prior apparatus noted above has the following drawback.
Among large size semiconductor wafers used recently, there are some that have a V-shaped notch formed peripherally thereof in place of the orientation flat. Such a notch has small dimensions; an opening angle approximately 90.degree. and a distance about 1.0 mm from its apex to an outer periphery of the wafer. To detect the position of such a notch in the conventional manner noted above, outer peripheral positional data must be collected from numerous sampling points by rotating the wafer stepwise through very small angles. This notch detecting operation would be time-consuming.